You know you get the dumb look on your face and is this damn thing working? Ethernet has activity indicators, you know the two lights on the RJ45 socket.

Well, we can do the same for Serial Ports remember that Arduino's are only 2 pins (rx and tx). 

Factoid: I hate messing with RS232 connectors. So where does it say that You must use DB-9/15/25? really nowhere.

So grab you an RJ45 Breakout Socket without magnetics from the web. So we have four (4) pairs to play with. BTW pairs are a good thing.

  1. Find the LED leads and check them with you DVM (diode check) this will be enough to lite them. find which one works both ways. We don't care about + or - so well refer to them as D1(1 or 2).
  2. Hook it up.
    1. Serial1(1) to 470 Ω resistor (for current limiter) R1(1)
    2. R1(2) to D1(1)
    3. D1(2) to Serial1(2)

WAIT, YOU SAY: How is this supposed to work? The LED is connected between two outputs (Rx & Tx); Duh?

Well get this,  both Rx and Tx are never both High or Low at the same time. So if Rx is high and Tx low then you get flow through one of the diodes, and when Tx is high and Rx low you get flow through the other diode.


Neat huh? So this is pure win-win.


Arduino Comports
Serial 0Serial 1Serial 2Serial 3
Arduinopins 0 (RX) and 1 (TX)
LeonardoUSBpins 0 (RX) and 1 (TX)
Megapins 0 (RX) and 1 (TX)pins 19 (RX) and 18 (TX)pins 17 (RX) and 16 (TX)pins 15 (RX) and 14 (TX)
Duepins 0 (RX) and 1 (TX)pins 19 (RX) and 18 (TX)pins 17 (RX) and 16 (TX)pins 15 (RX) and 14 (TX)


Stay Tuned In. More To Come
  ~~ Cris H.

Back to the Index